Studies Of Physicochemical Properties And Extarction Performance Of PEG-functionalized Ionic Liquids

Due to the unique physicochemical properties such as negligible vapor pressure,high thermal stability and strong solubilization capacity,ionic liquids?ILs?have been used in fuel cells batteries,organic reactions and composite materials.As greener solvents to replace volatile organic solvents,ILs have been also widely used in the extraction and separation processes.However,there are still a number of problems to study,such as the use of extracting agents in the extraction of metal ions,recovery of target extracts and recycle utilization of ILs.As a part of the researches of the project supported by the National Natural Science Foundation of China?No.21273062?,a new class of PEG functionalized ionic liquids have been synthesized,their physicochemical properties have been determined and their application in the extraction of rare earth metal ions and Vitamin B₆ have been explored in this wok.The major contents are as follows:1.Five PEG functionalized ionic liquids?[PEG200?mim?2][Tf₂N]₂,[PEG400?mim?2][Tf₂N]₂,[PEG600?mim?2][Tf₂N]₂,[PEG800?mim?2][Tf₂N]₂,[PEG1000?mim?2][Tf₂N]₂?were designed and prepared.Physicochemical data of density,viscosity,and conductivity were determined in the temperature range from 298.15 K to 348.15 K.It was shown that with increasing temperature,densities of the ILs slightly decreased,their viscosities decreased markedly,while their electrical conductivities increased significantly.The temperature dependence of the ILs densities could be described by the Tait equation,and both the temperature dependence of the viscosities and conductivities of the ILs could be described by VFT equation.The molar volume,standard molar entropy,and lattice energy were estimated for the ILs by empirical equations.Ionicity of the ILs was also discussed by the Walden equation.2.The extraction performance of the PEG functionalized ILs was studied for rare earth metal ions.Factors influencing the extraction process such as phase volume ratio,equilibrium time,p H value of aqueous phase,alkyl chain length of the ionic liquids and temperature of the system were examined systematically.It was found that under optimal conditions,the single-step extraction efficiency was greater than 96.8 % for the studied 11 kinds of rare earth metal ions Sc?III?,La?III?,Ce?III?,Y?III?,Nd?III?,Sm?III?,Gd?III?,Dy?III?,Ho?III?,Yb?III?and Lu?III?.After the extraction,the rare earth metals could be stripped from the ILs phases by using dilute aqueous oxalic acid,and the ILs would be recovered and reused in the next extraction process.The driving force for the extraction of rare earth metal ions by these ILs could be ascribed to the strong interaction between metal ion and oxygen atom of ether oxygen group of the ILs.3.The extraction of Vitamin B₆ from aqueous solution was studied by using ionic liquids as solvents.The effects of phase volume ratio,equilibrium time,pH value of aqueous phase,alkyl chain length of the ionic liquids and temperature of the system on the solvent extraction process were investigated in detail.The results indicated that the single-step extraction efficiency could reach to 90%,which increased with increasing pH of the aqueous phase and attained the maximum at pH 3.8.Vitamin B₆ could also be stripped from the ionic liquid phase by 5 mol/L hydrochloric acid solution.